The present invention relates to an electrophotographic apparatus. More particularly, the present invention relates to an electrophotographic apparatus whose maintenance can be easily and economically performed.
An electrophotographic apparatus includes, as is already known, a photoreceptor which is charged by a charging device, and on which an electrostatic latent image is formed by an exposing device, a developing device which employs toner to form a toner image from the electrostatic latent image, a transferring device for transferring the toner image onto a sheet, a fixing device for fixing the transferred toner image, a cleaning device for cleaning toner remaining on the photoreceptor after the transfer of the toner image, and a charge removing device for removing the charge remaining after the formation of the latent image.
Such component parts constituting an electrophotographic apparatus have their own lives. For instance, the photoreceptor is vulnerable to damage because it is subjected to corona discharge by the charging device, exposed to strong light by the exposing device, and kept in contact with ozone or nitrogen oxides generated by corona discharge or toner. The photoreceptor is also vulnerable to wear because of friction caused by its contacting with a sheet during transfer or with the cleaning device. The developing device may reach the end of its life when, for instance, its charging efficiency is degraded by part of the toner conveyed by a toner conveying carrier adhering to a surface of the carrier, when the carrier itself is worn, or when the device is unable to stably obtain image densities since a developing roller is contaminated with impurities contained in toner and, simultaneously, the device needs a further supply of toner. Also, component parts, such as the cleaning device, which include consumables, such as brushes formed by bundles of fine fiber, have their lives because of this fact.
In order to stably obtain images of high quality, therefore, due attention has to be paid to the checking and the replacement of various component parts, and to the replacement and the supply of consumables, so that each of the component parts is always able to maintain the required level of performance. For this purpose, the conventional practice has been such that various component parts are arranged in such a manner that they can be detached from the main body of the apparatus by detachment mechanisms, and a service person visits the user each time a certain period has passed so as to provide maintenance services such as the checking, the cleaning, and/or the replacement of component parts, and the supply of consumables.
This conventional practice is advantageous in that only the part whose life has ended can be, for instance, replaced. On the other hand, the practice inevitably requires a large number of visits. It also requires a large number of detachment mechanisms for detaching and reattaching component parts from and to the main body of the apparatus, thereby complicating the entire apparatus. In addition, if, during the mounting of component parts, their relative positions are distorted, this leads to the risk of the production of images of good quality being hindered. In order to avoid this risk, the mounting operation must be performed precisely and carefully, thereby making the operation one which is complicated and which requires skill and time. Another disadvantage is that since component parts are more or less contaminated by toner, when they are being detached or reattached, this inevitably results in the area surrounding the apparatus or clothing worn by people becoming contaminated.
A means has been proposed, therefore, to eliminate these disadvantages. According to this proposal, the main parts in the periphery of the photoreceptor, which include the developing device, the charging device and the cleaning device, and which are vulnerable to damage or wear, are arranged in such a manner that they can be detached from and reattached to the main body of the apparatus while they form a completely integral structure. When this structure is replaced, operations such as the replacement of the photoreceptor, the cleaning of the charging device or the like, the replacement of the cleaning device, the disposal of toner removed from the surface of the photoreceptor, and the supply of toner can be performed all at one time.
With this means, therefore, the maintenance operation is simplified. In addition, there is no risk of the area surrounding the apparatus becoming contaminated, while easy maintenance service is made possible. However, a problem arises in that the shortest of the service lives of these component parts integrated in the structure determines the life of the entire structure. For example, if the service life of an organic photoconductive type photoreceptor reaches an end after the production of about 50 thousand printed sheets, the associated developing device, which is, when the service life of the photoreceptor ends, still capable of producing 150 thousand sheets during the rest of its life, must also be abandoned and replaced. This results in high maintenance cost. In addition, the amount of toner initially stored in the integral structure must be great enough to comply with the number of sheets that the associated component part, e.g., the photoreceptor, is capable of producing throughout its service life. If such a great amount of toner is stored, the toner itself may absorb moisture, or blocking due to heat may occur, thereby leading to the risk of image quality degradation. In order to avoid this risk, the mechanism for stirring toner, the mechanism for conveying toner, etc. have to be made large and complicated.